Conventionally, shot blasting is used for removing rust, burrs, scales, or a composition for coating surfaces of products by projecting shot, such as small rigid spheres, at the products. For the shot blasting, a centrifugally projecting machine is used. It can use centrifugal force to continuously project shot by means of a high-speed rotation of an impeller that has a plurality of blades. For example, Patent Document 1 discloses a centrifugally projecting machine for projecting abrasive grains. This machine is comprised of an impeller having 4 to 12 blades, wherein the blades are radially disposed between rotating plates having a circular shape, and a spinning body that is rotatably mounted on the machine, so that the inner ends of the blades define a space having a substantially cylindrical shape of a diameter of 135 to 170 mm.
It is also comprised of a distributor concentrically arranged in the space defined in the spinning body. The distributor has a cylindrical shape, and has a bottom plate. The distributor extends over the axial length of the spinning body, and has the same number of slit-like openings as that of the blades. The openings are circumferentially disposed with substantially equal intervals.
It is also comprised of a control cage independently fixed at the clearance between the inner ends of the blades and the outer surface of the distributor.
Further, this centrifugally projecting machine is designed so that shot are provided for the blades from the distributor through a hole of the control cage, and then are accelerated and projected at a product to be processed by the blades. However, some of the shot sometimes spill from the clearance between the distributor and the control cage. Thus, liners must be put on the inner side of a cover (a housing) surrounding the impeller to prevent the cover from being abraded by the shot projected in a direction that differs from the direction for processing a target product.                Patent Document 1: Japanese Patent Laid-open Publication No. H9-150369        